Embodiments of the present disclosure are related to wind turbines, and more particularly to a system and method for controlling wind turbines.
Generally, a wind turbine includes a rotor having multiple blades. Wind turbines used to provide electrical power to a utility grid often have large rotors with blade diameters of 80 meters or more. Asymmetric loading across wind turbine rotor occurs due to vertical and horizontal wind shears, yaw misalignment, and turbulence. Vertical wind shear, yaw misalignment, and natural turbulence are among the primary drivers of asymmetric loads on a wind turbine rotor. These loads, along with the loads from vertical and/or horizontal wind shears, are contributors to extreme loads and the number of fatigue cycles accumulated by a wind turbine system.
Yaw misalignment can occur during turbulent wind periods when the wind shifts direction rapidly and maintains the new wind direction for a period of time. Static and cyclic loads induced in the wind turbine in this condition are a driving factor in the design of many of the wind turbine components. The components are necessarily designed to withstand the loads induced by extreme yaw misalignment. Making such robust components to be able to withstand those loads is expensive and operating components that suffer a reduced life span due to the cyclic nature of the loads is expensive and time-consuming.
During such load periods some known wind turbine systems attempt to counter the loading effects by manipulating a blade pitch control system or yaw control system to facilitate reducing loads if the misalignment is relatively small or short lived. Most wind turbine systems resort to shutting down the wind turbine if the yaw misalignment exceeds a threshold.
However, an uncontrolled shutdown of the wind turbine may present conditions, such as, but not limited to, overspeed of the rotor and extreme loads that can occur in a hub or a tower top, or blade flap moment.